1. Field of the Invention
The present invention generally relates to filter design and more particularly to a resistor and capacitor filter circuit.
2. Description of Related Art
Over the last decade or so, numerous current conveyor-based second-order or high-order filters have been reported. Using signal-flow graph approach, several nth-order transfer function syntheses using current conveyors have been proposed. For example, four second-generation current conveyors, two floating and one grounded capacitors, and seven floating and two grounded resistors have been utilized to realize a third-order all-pass current conveyor filter. Four second-generation current conveyors, two floating and one grounded capacitors, and seven floating and one grounded resistors have been utilized to realize a third-order all-pass current conveyor filter. In order to let all the capacitors be grounded, five current feedback amplifiers (CFAs), each of which is equivalent to a plus-type second-generation current conveyor following a voltage buffer, and a few resistors, i.e., eight floating and three grounded resistors in addition to three grounded capacitors are necessary for synthesizing a third-order all-pass filter. It is apparent that the use of so many resistors used to synthesize the above all-pass filters is a problem and needs to be reduced to the minimum since the implemented area in an integrated circuit of a resistor is rather large and much bigger than several transistors.
Since the addition and subtraction operations of voltage-mode signals needs the realization, respectively, of addition and subtraction circuits, unlike in the case of current-mode signals, two recently introduced active elements, namely, differential difference current conveyors (DDCCs) and fully differential current conveyors (FDCCIIs), with the intrinsic voltage addition and subtraction ability, have become very attractive to be used in the design of voltage-mode filters.
On the other hand, the advantages of the Analytical Synthesis Methods have been clearly and effectively demonstrated recently in the realization of high-order current/voltage-mode Operational Trans-conductance Amplifier and Capacitor (OTA-C) filters, where a complicated nth-order transfer function is manipulated and decomposed by a succession of innovative algebraic operations until a set of simple equations are produced, which are then realized using n integrators and a constraint circuitry. In fact, the new Analytical Synthesis Method can be used in the design of any kind of linear system with a stable transfer function.